Bone grafting is possible because bone tissue, unlike most other tissues, has the ability to regenerate completely if provided the right environment, including a space into which to grow, or a matrix to grow on. As native bone grows, it replaces the graft material, so that over time, the graft is replaced by a fully integrated region of new bone.
Bone regeneration occurs through osteoinduction, a process in which connective tissue is converted into bone by an appropriate stimulus. Osteoinduction allows bone formation to be induced even at non-skeletal sites and is initiated by bone morphogenetic proteins (BMP).
The ideal bone graft material would be a strong, porous biocompatible material infused with BMP that did not cause inflammation and would ultimately be reabsorbed into the body as it is replaced by natural bone.
Bone is composed of 50 to 70% inorganic mineral, 20 to 40% organic collagen matrix, 5 to 10% water, and <3% lipids. The inorganic mineral content of bone is mostly hydroxyapatite [Ca.sub.10(PO.sub.4)6(OH).sub.2]. The inorganic mineral provides the mechanical strength and rigidity, whereas the organic collagen matrix provides elasticity and flexibility.
Demineralized bone matrix (DBM) is allograft bone, i.e., bone from other humans, that has had the inorganic, mineral material removed, leaving behind the organic collagen matrix and the BMPs that induce osteoinduction. DBM is conducive to osteoinduction, but lacks the load bearing strength. It is typically used with a 2-4% hyaluronate carrier as a paste or putty to fill a space needing bone, and allows real bone to grow into it within weeks to months.
The present invention provides a system and method of producing custom bone grafts that are made of a porous, biocompatible material infused with BMPs that can be used as ink in a 3-D printer to produce bone grafts of any desired shape.